The present application relates to a subject matter described in U.S. Ser. No. 09/793,402, a commonly owned U.S. Patent Application which was filed on Feb. 27, 2001, by Y. Jiboshi, M. Gosuga, T. Nogi, T. Shiraishi and N. Tokuyasu, and entitled xe2x80x9cEmission Control Device for Cylinder Fuel Injection Enginexe2x80x9d. The disclosure of the above-identified commonly owned U.S. Patent Application is herein incorporated by reference.
The present invention relates to a cylinder injection engine directly injecting a fuel into a combustion chamber of the engine.
In a cylinder injection engine, it is not possible to inject a fuel while an exhaust value is in open position. Therefore, injection of fuel is performed during an intake stroke and a compression stroke. In an intake stroke injection, fuel is injected while an intake valve is in open position, and fuel is substantially uniformly mixed with air within the cylinder to form a homogenous mixture. In general, effecting spark ignition by an ignition plug for the homogenous mixture for combustion will be referred to as homogenous combustion.
On the other hand, in a certain driving condition of the cylinder injection engine, fuel injection is effective during the compression stroke for forming a stratified charge mixture, in which a rich mixture is formed in the vicinity of the ignition plug for assuming spark ignition performance and a lean mixture is formed around the rich mixture. Such combustion mode will be referred to as stratified charge combustion.
It has been known to drive the engine with switching combustion modes between the homogenous combustion and the stratified charge combustion. One of important factors as switching condition is an engine coolant temperature. When the engine coolant temperature becomes about 80xc2x0 C., after warming up of the engine, the stratified charge combustion is permitted. Accordingly, under a condition where the engine coolant temperature is low, including starting up of the engine, the homogenous combustion is performed. However, an exhaust gas discharged from the cylinder injection engine is purified by a catalytic converter disposed in an exhaust pipe and then discharged from the exhaust outlet. However, since a temperature of the catalytic converter does not go up to sufficient high temperature for several minutes from starting of the engine, a conversion performance for purifying the exhaust gas is held low. Furthermore, upon starting up of the engine, since a cylinder wall surface or peripheral air temperatures are low, atomization performance of the fuel is low. Therefore, ignitionability is low to degrade combustion condition or even to cause a misfire. In order to attain sufficient ignitionability, fuel in four to five times of necessary amount is injected to increase atomized fuel amount. However, in this method, fuel not contributed for combustion upon starting up of the engine is discharged through an exhaust valve and passes through the low temperature catalytic converter without purification to be discharged to the atmosphere in unpurified form. In the recent years, emission control regulations in Europe and the United States increases strictness. Therefore, it is becoming essential to make the exhaust gas clean even upon starting up of the engine.
As a technology for promoting atomization of fuel, JP-A-9-79066 discloses compensation of a fuel injection timing depending upon the engine coolant temperature and a fuel pressure upon starting up of the engine. According to the disclosed technology, when the engine coolant temperature is low, the fuel injection timing is set at the intake stroke to provide sufficient period for atomization of the fuel. Also, in JP-A-10-176574 discloses injection from a sub-injector installed in an air intake pipe when the engine coolant temperature and the fuel pressure are lower than or equal to predetermined values upon starting up of the engine. In the disclosed technology, by injecting the fuel into the air intake pipe, longer distance to the combustion chamber is provided for providing longer period for atomization of the fuel. In these method, the air/fuel mixture to be formed within the engine cylinder is homogenous mixture and accordingly, combustion mode is homogenous combustion.
On the other hand, when homogenous combustion is performed in the condition while the engine is not sufficiently warmed, a large amount of unburned fuel component, i.e. HC (hydrocarbon) tends to be discharged. The reason is that non-atomized fuel due to low cylinder wall surface temperature, may deposit on the cylinder wall surface or peripheral surface of the piston.
Therefore, it is an object of the present invention to provide a method of starting a cylinder injection engine which can certainly provide good engine start-up characteristics and can clean an exhaust gas.
According to the first aspect of the present invention, a starting method is provided for a cylinder injection engine which includes a combustion chamber introducing air, a fuel injection valve directly injecting a fuel into the combustion chamber, a piston varying volume of the combustion chamber, and a starter for starting up the engine. The method comprises the steps of:
starting the engine; and
injecting a fuel in a compression stroke when the starter is actuated for starting up the engine.
According to the second aspect of the present invention, a fuel pressure is set within a range of 2 to 4 MPa, or greater than or equal to 6 MPa.
According to the third aspect of the invention, a fuel is injected during a compression stroke of the cylinder after actuating the starter is actuated for starting up the engine, and making judgment that the cylinder is in compression stroke.
According to the fourth aspect of the present invention, the engine has an EGR piping connecting an exhaust pipe to an air intake pipe and an EGR valve, the EGR valve is opened while the starter is actuated for starting up the engine, and a fuel is injected during a compression stroke.
According to the fifth aspect of the invention, the engine has a variable valve mechanism for controlling opening and closing timing of an intake valve, a valve closing timing of the intake valve is controlled at the maximum retard position while the starter is actuated for starting up the engine and a fuel is injected during a compression stroke.